Cardiac pacing therapies deliver pacing pulses to a patient's heart to treat various cardiac conditions, such as bradycardia, tachycardia and heart failure. Depending on the location of the cardiac pacing electrodes and the pacing pulse energy delivered, non-cardiac, excitable tissue may be inadvertently captured by the cardiac pacing pulses, causing unwanted stimulation of extracardiac nerve or muscle. For example, during cardiac resynchronization therapy (CRT), cardiac pacing pulses may be delivered to the left ventricle to restore synchrony between the right and left ventricles of the heart. The left ventricle is typically paced using electrodes carried by a transvenous lead extending through a cardiac vein along the left ventricle. These electrodes may be in proximity to portions of the phrenic nerve that innervate the diaphragm. Cardiac pacing pulses delivered to the left ventricle may inadvertently capture the phrenic nerve and thus cause diaphragm contraction. Besides phrenic nerve stimulation, intercostal muscles or other excitable tissue in proximity to a cardiac electrode may be stimulated at high enough energy to cause depolarization or “capture” of the excitable tissue, causing muscle twitching, contraction, pain or discomfort.
Extracardiac stimulation may cause pain, discomfort or annoyance to the patient. When the patient feels the extracardiac stimulation, he or she may schedule an appointment with a doctor to address the situation. A clinician will typically adjust the parameters controlling pacing pulse delivery by reprogramming the cardiac rhythm management device. In some cases, the cardiac lead may need to be repositioned in order to eliminate extracardiac stimulation. A need remains for an apparatus and method for automatically detecting extracardiac stimulation that captures non-cardiac tissue to allow the extracardiac capture to be mitigated.